1. Field of the Invention
The present invention relates to a film having optical anisotropy (optically anisotropic film) that is obtained using a polymerizable liquid crystal composition containing an antistripping additive, and a liquid crystal display device including the optically anisotropic film.
2. Description of the Related Art
A polymerizable liquid crystal compound is used for an optically anisotropic film such as a polarizing plate, a polarized light reflecting plate and a retardation film (Patent literature No. 1). The reason is that the compound shows optical anisotropy in a liquid crystal state and the anisotropy is immobilized by polymerization. Optical characteristics required for the optically anisotropic film are different depending on a purpose, and therefore a compound having characteristics fit for the purpose is required. Control of the anisotropy is difficult alone by a compound used for an optical isomer in many cases. Therefore, such a compound may be occasionally used in the form of a composition in combination with various compounds.
The polymerizable liquid crystal composition may be occasionally used in the form of ink prepared by adding an organic solvent in order to adjust coating properties. In order to manufacture a film having optical anisotropy by using the polymerizable liquid crystal composition, the polymerizable liquid crystal compound, a photopolymerization initiator, a surfactant and so forth are dissolved into the organic solvent to prepare ink in which solution viscosity, levelability or the like is adjusted. The ink is applied to a substrate subjected to alignment treatment to dry a solvent to align a polymerizable liquid crystal composition on the substrate. Next, the composition is irradiated with ultraviolet light and polymerized, thereby immobilizing an alignment state.
The present inventors have so far found a polymerizable liquid crystal compound allowing formation of uniform homeotropic alignment on a glass substrate or a plastic substrate without forming an alignment layer on a support substrate using the polymerizable liquid crystal compound, and having excellent adhesion (Patent literature Nos. 6 and 7).
Moreover, as an apparatus allowing an observer to recognize a three-dimensional image, an image display apparatus is known in which the apparatus include an image generation part for displaying an image for a right eye and an image for a left eye on different regions, respectively, and a polarization axis control plate for mutually orthogonalizing polarization axes of polarized light entered into two different regions (see Patent literature Nos. 2 to 4, for example). A retardation film used for the three-dimensional image display apparatus is mainly formed into a patterned retardation film prepared by applying a polymerizable liquid crystal compound having a liquid crystal phase as a retardation material onto an alignment layer subjected to patterned alignment treatment, and photocuring the applied material. The polymerizable liquid crystal composition mainly used for the patterned retardation film forms homogeneous alignment, and an alignment layer is substantially necessary to form the homogeneous alignment. For the alignment layer, polyimide obtained by heating and imidizing polyamic acid is widely used, but imidization requires heating to 200° C. or higher, and thus use of such polyimide for a plastic substrate is quite difficult. A method for directly rubbing a plastic substrate is also applied without using polyimide, special facilities are necessary for removing dust and static electricity generated by the rubbing.
Consequently, a photoalignment technique also has been recently applied in which a certain polymer solution is applied to a plastics substrate, and then the applied material is irradiated with polarized ultraviolet light to provide the material with alignment ability. However, the technique has a problem of insufficient adhesion and durability of an interface between an alignment layer and a liquid crystal composition layer in a patterned retardation film including only the polymerizable liquid crystal compound. The insufficient adhesion and durability may occasionally cause, for example, when a protective film is stuck on the patterned retardation film for preventing scratching or dirt or the like during transportation, deposition of a liquid crystal composition layer of the patterned retardation film onto an adhesive surface side of the protective film upon removing the protective film to damage the patterned retardation film. In order to solve such a problem, a patterned retardation film formed of a liquid crystal composition layer containing an antistripping additive has been desired (see Patent literature No. 5). In Patent literature Nos. 6 and 7 as described above, study has been conducted on adhesion between a liquid crystal composition layer in homeotropic alignment, but no study has been conducted on adhesion and durability of a liquid crystal composition layer in homogeneous alignment. In particular, no study has been made on durability under a severe environment such as high humidity and high temperature.